Microwave signals are broadcast from communication satellites in various frequency bands (e.g. C band and Ku band) to be received in television receive only (TVRO) systems. Each microwave signal is typically linearly polarized in one of two possible orientations whose electric field vectors are orthogonal to one another. Adjacent television channel signals are typically orthogonal to one another to enhance channel isolation. Orthogonal linearly polarized signals may be received by rotatable receiving systems configured for repeated alignment with the signal polarization or in fixed receiving systems designed to remain in a fixed orientation after an initial alignment. Fixed systems have become increasingly attractive as more satellites, and hence their orthogonal signals, are maintained in absolute geophysical alignment.
U.S. patents of interest in reception of orthogonal linearly polarized signals include U.S. Pat. Nos. 2,825,032; 3,358,287; 3,388,399; 3,389,394; 3,458,862; 3,573,838; 3,668,567; 3,698,000; 3,864,687; 4,041,499; 4,117,423; 4,414,516; 4,528,528; 4,544,900; 4,554,553; 4,595,890; 4,672,388; 4,679,009; 4,707,702; 4,755,828; 4,758,841; 4,862,187; 4,890,118; 4,903,037; 4,951,010; 4,996,535; 5,043,683; 5,066,958 and 5,107,274. Apparatus intended for reception of orthogonal linearly polarized signals are supplied by SPC Electronics under the designations of models DPS-710 Series and DPS-710R Series and by Pro Brand International under the designation of Aspen Eagle LNBF 1000.